Method and apparatus for purifying sea water

ABSTRACT

Sea water contaminated with suspended organic matter and the like can be purified by expanding a mixture of the water with air so as to generate a froth, and letting the froth carrying the impurities overflow from a tubular riser attached to the expansion vessel while purified water is drawn off from the bottom of the vessel. The froth is stabilized by maintaining a layer of more alkaline liquid on the inner wall of the riser. The apparatus employed uses a rotating nozzle for continuously rinsing the wall of the riser with a liquid more alkaline than the froth, such as the original sea water prior to its being mixed with air.

United States Patent Hiickstedt et al.

METHOD AND APPARATUS FOR PURIFYING SEA WATER Inventors: GuidoHiickstedt, Starnberg;

Hermann Jakobs, Seewiesen, both of Germany Max-Planck-Gesellschaft, zurForderung der Wissenchaften e.v., Gottingen, Germany Filed: Mar. 13,1972 Appl. No.: 234,161

Assignee:

Foreign Application Priority Data Mar. I5, 1971 Germany P 21 12 401.6

US. Cl 210/44, 210/221, 209/170 Int. Cl... B03d 1/00 Field of Search210/44, 221;

References Cited UNITED STATES PATENTS 8/1948 Lawrason .1 210/443,669,883 6/1972 Huckstedt 2lO/44 Primary ExaminerFrank A. Spear, Jr.Assistant ExaminerThomas G. Wyse Attorney-Kurt Kelman et al.

[57] ABSTRACT Sea water contaminated with suspended organic matter andthe like can be purified by expanding a mixture of the water with air soas to generate a froth, and letting the froth carrying the impuritiesoverflow from a tubular riser attached to the expansion vessel whilepurified water is drawn off from the bottom of the vessel. The froth isstabilized by maintaining a layer of more alkaline liquid on the innerwall of the riser. The apparatus employed uses a rotating nozzle forcontinuously rinsing the wall of the riser with a liquid more alkalinethan the froth, such as the original sea water prior to its being mixedwith air.

9 Claims, 2 Drawing Figures 1 PATENTEDNBV 131975 3.772.192 SHEET 10F 2Fig.1

METHOD AND APPARATUS FOR PURIFYING SEA WATER This invention relates tothe purification of contaminated water, and particularly to a method ofpurifying sea water contaminated with ions of a heavy metal and- /orsuspended organic matter, and to apparatus for performing the method.

It is known to purify sea water in 'continuous flow by mixing the waterwith air in an amount sufficient to generate a froth which is enrichedwith the impurities to be removed, and to separate the froth from theremainder of the water, thereby purifying the latter. The procedure isclosely related to the known method of ore concentration by flotation.Because of its salt content, sea water tends to froth or foam under theaction of air even in the absence of surface active agents.

When trace amounts of suspended organic matter of relatively highmolecular weight or minute amounts of heavy metal ions such as copperare present in the raw water, the froth accumulates the contaminants atthe liquid-gas interface of the bubbles in the froth. The purifyingeffect is lost if the froth collapses or is otherwise disturbed. It isessential, therefore, properly to control all operating variables, suchas the relative amounts of air and sea water, the air pressure, and thelike, to keep the foam stable.

It has been found that it is difficult to maintain the required balanceof process variables, and the amount of residual impurities in therecovered water rises in the known methods at such a rate as to makecontinuous water purification impractical.

It is the primary object of the present invention to modify the knownmethod of water purification by froth separation so that it providesconsistently favorable results in continuous operation.

Another important object is the provision of apparatus for performingthe improved method.

It has now been found that foam generated from sea water in the mannerdescribed can be stabilized, and that water can be purified incontinuous operation if the froth is continuously introduced into thebottom portion of a container bounded by upright walls and continuouslyremoved from the top portion of the container while a concentration ofnegative charges greater than in said froth is maintained in thecontainer adjacent the upright wall.

If this distribution of negative electric charges is maintained byrinsing the wall with a suitable liquid, and the liquid flows downwardalong the rinsed wall, the liquid has no harmful effect on the rinsingfroth although moving in the opposite direction.

The froth generated by' expanding a mixture of contaminated sea waterand air is invariably more acid than the sea water originally fed to thepurification apparatus and may thus be employed as the wall rinsingliquid. The decreased pH of aerated sea water is believed due tooxidation of such organic matter as protein in human excrements and insubstances originating from dead animals and plants. The importance ofusing a rinsing liquid more alkaline than the froth is readilydemonstrated'by slightly acidifying the raw sea water which otherwisestabilizes the froth. The froth rapidly collapses in contact with themore acid rinsing liquid.- It is stabilized by an amount of morealkaline raw water which is a very small fraction of the total waterprocessed..

Apparatus suitable for performing the method may include an expansionvessel, a mixing device for intimately mixing the water to be purifiedwith air, a feeding device for feeding the resulting mixture of waterand air to the expansion vessel under a pressure higher than thepressure in the vessel, and an outlet on the bottom portion of thevessel for withdrawing purified water while maintaining a liquid levelin the vessel. A tubular riser extends upwardly from the vessel, and thespace enclosed therein communicates with the vessel for receiving thefroth which is generated by expansion of the water/air mixture in thevessel and rises above the liquid level. The froth is released from aportion of the riser space remote from the expansion vessel in an upwarddirection. A rinsing device is provided for applying a film of liquid toan inner face of the riser while keeping the remainder of the space inthe riser substantially free from the liquid.

Additional features, other objects, and many of the attendant advantagesof this invention will readily become apparent from the followingdetailed description of a preferred apparatus of the invention and ofthe operation of this apparatus when considered in connection with theappended drawing inwhich:

FIG. I shows the apparatus in fragmentary side elevation and partly insection; and

FIG. 2 shows the portion of the apparatus omitted from FIG. 1 inelevational section on a larger scale.

Referring now to the drawing in detail, and initially to FIG. 1, thereis seen an upright, cylindrical expansion vessel 1. A feed pipe 2connects the top portion of the vessel 1 with a water jet pump 3,conventional in itself, which draws ambient atmospheric air through anintake 4 and mixes itwith a stream of water supplied under adequatepressure by a non-illustrated pump. The suction pipe of the pump isconnected to a source of the sea water to be purified in a manner notillustrated since entirely conventional.

The liquid level in the expansion vessel 1 is maintained by an outletpipe 5 extending upward from the bottom portion of the vessel 1 andterminating in a nozzle 6 at its upper, free end. The nozzle 6 isthreadedly mounted in the wall of a chamber 7 which spacedly envelopsthe nozzle 6 to catch liquid sprayed from the nozzle and is open to theatmosphere through a spout 8.

The top end of the expansion vessel 1 tapers conically to a coaxialtubular riser 11 consisting of several axial sections which are attachedto the vessel 1 and to each other by flanges 9, 10. The top end of theriser 11, shown in FIG. 2, is provided with a cover 13 from which anoverflow pipe 12 may release material to the atmosphere or a collectingtank.

A hollow cylinder 14 coaxial with the riser l 1 and the vessel 1 extendsupward from the cover 13. Two sealed bearings 15 are axially spaced inthe cylinder 14 and sealingly receive a tubular member 16 for coaxialrotation in thecylinder 14. The member 16 is axially sealed at the topand bottom, but has two lateral orifices.

One of the orifices at the bottom end of the tubular member 16 in thespace within the riser 11 is sealingly engaged by a nozzle 17. Thenozzle is a tube extending obliquely from the lower orifice of themember 16 in a radial and downward direction. The free, open end of thenozzle 17 is located closely adjacent the overflow edge of the riser 11in the cover 13, and is downwardly offset from the edge a very smalldistance.

The other lateral orifice 21 of the member 16 communicates outside theriser space with a chamber 18 axially bounded in the cylinder 14 by thetwo bearings 15. A supply pipe 22 is connected with the chamber 18 asfar as illustrated, and the non-illustrated end of the pipe 22 draws rawsea water from the pump, not shown, which feeds water to the water jetpump 3.

The upper, closed end of the tubular member 16 is fastened to the outputshaft 19 of a gear motor 20 mounted on nonillustrated supportingstructure. When the drive motor 20 is energized, the tubular member 16is turned about its axis as indicated by a curved arrow, and the free,open end of the nozzle 17 sweeps along the inner wall face of the riser11 in a continuous arc.

During operation of the illustrated device, a continuous, thin film ofrelatively alkaline sea water is maintained on the inner wall face ofthe riser 11 by the rotating nozzle 17 whose water supply is suitablycontrolled by a non-illustrated valve in the pipe 22.

The pressure of the water entering the jet pump 3 is similarlycontrolled to raise the pressure of the water- /air mixture fed to thevessel 1 through the pipe 2 well above the atmospheric ornear-atmospheric pressure in the expansion vessel. The air bubbles inthe intimate water/air mixture expand in the vessel 1 so that a frothforms continuously on the liquid surface, the earlier formed froth beingpushed upward by froth newly formed in the water entering the vessel 1through the feed pipe 2 and withdrawn from the vessel through the outletpipe 5 with a much smaller air content and stripped of a significantportion of its impurities.

Because of chemical interaction between the oxygen in the air drawn intothe water jet pump 3 and the impurities in the water, the froth is ofsignificantly lower pH value than the raw sea water which wets the innerwalls of the riser 11. The more alkaline film on the walls substantiallyincreases the stability of the froth so that the apparatus illustrated,when once adjusted for adequate water pressure in the water jet pump 3,can be run continuously and continuously removes the impurities in thesea water with the froth released through the overflow pipe 12. Purifiedwater is discharged from the spout 8.

if the nature of the contaminated water is sufficiently different fromthat of sea water as not to be acidified by the action of the admixedair, the more alkaline film of liquid on the inner surfaces of the risermay be provided in any other desired manner, as by connecting the supplypipe 22 to a tank containing very dilute sodium carbonate solution.

As is inherent in the described mode of operation, devices other thanthe nozzle arrangement of FIG. 2 may be employed for maintaining ahigher concentration of negative charges adjacent the inner face of theriser 11 than prevails in the froth, and the nozzle arrangement thuswill be understood to be merely exemplary of suitable apparatus.Provisions, of course, must be made not to let the more alkaline liquidpermeate the froth.

It will be understood, therefore, that the foregoing disclosure relatesonly to preferred embodiments of the invention and that is is intendedto cover all changes and modifications of the example of the inventionherein chosen for the purpose of the disclosure which do not constitutedepartures from the spirit and scope of the invention set forth in theappended claims.

We claim:

1. A method of purifying contaminated raw water which comprises:

a. mixing a flowing body of said water with an amount of air sufficientto cause formation of a froth on the surface of said water;

b. continuously introducing said froth into the bottom portion of acontainer bounded by an upright wall;

0. continuously removing said froth from a top portion of saidcontainer;

d. rinsing said wall with a liquid having a pH value higher than the pHvalue of said froth in an amount sufficient to maintain in saidcontainer adjacent said wall thereof a concentration of negativeelectric charges greater than the concentration of negative electriccharges in said froth; and

e. recovering the water separated from said froth.

2. A method as set forth in claim 1, wherein said raw water is sea watercontaminated with ions of a heavy metal, said ions accumulating in saidfroth and being removed therewith from said water.

3. A method as set forth in claim 1, wherein said raw water is sea watercontaminated with suspended organic matter, said organic matteraccumulating in said froth and being removed therewith from said water.

4. A method as set forth in claim 1, wherein said liquid is constitutedby a portion of said raw water free from said air.

5. Water purification apparatus comprising, in combination:

a. an expansion vessel;

b. mixing means for intimately mixing the water to be purified and air;

c. feeding means for feeding the resulting mixture of water and air tosaid expansion vessel under a pressure higher than the pressure in saidvessel, whereby said mixture expands in said vessel;

(1. outlet means on a bottom portion of said vessel for withdrawingpurified water from said vessel while maintaining a liquid level in saidvessel;

e. a tubular riser upwardly extending from said vessel and enclosing aspace, said space communicating with said vessel for receiving frothgenerated by expansion of said mixture in said vessel, said froth risingabove said level;

f. releasing means for releasing said froth from a portion of said spaceupwardly remote from said vessel; and

g. rinsing means for applying a film of liquid to an inner face of saidriser while keeping the remainder of said space substantially free fromsaid liquid.

6. Apparatus as set forth in claim 5, wherein said rinsing means includea nozzle member directed toward a portion of said inner facecontiguously adjacent said releasing means and offset from the sametoward said level.

7. Apparatus as set forth in claim 6, wherein said riser has an uprightaxis, said inner face extends about said axis, and said rinsing meansinclude rotating means for rotating said nozzle member about said axisand for thereby sequentially directing said liquid to portions of saidinner face angularly offset relative to said axis.

8. Apparatus as set forth in claim 7, wherein said rotating meansinclude a tubular member elongated in the direction of said axis, drivemeans for rotating said tubular member about said axis, said tubularmember having respective orifices in said space and outside said ingmeans include a water jet pump and means for connecting said water jetpump to a source of the water to be purified and to ambient air, saidfeeding means connecting said pump to said expansion vessel.

2. A method as set forth in claim 1, wherein said raw water is sea watercontaminated with ions of a heavy metal, said ions accumulating in saidfroth and being removed therewith from said water.
 3. A method as setforth in claim 1, wherein said raw water is sea water contaminated withsuspended organic matter, said organic matter accumulating in said frothand being removed therewith from said water.
 4. A method as set forth inclaim 1, wherein said liquid is constituted by a portion of said rawwater free from said air.
 5. Water purification apparatus comprising, incombination: a. an expansion vessel; b. mixing means for intimatelymixing the water to be purified and air; c. feeding means for feedingthe resulting mixture of water and air to said expansion vessel under apressure higher than the pressure in said vessel, whereby said mixtureexpands in said vessel; d. outlet means on a bottom portion of saidvessel for withdrawing purified water from said vessel while maintaininga liquid level in said vessel; e. a tubular riser upwardly extendingfrom said vessel and enclosing a space, said space communicating withsaid vessel for receiving froth generated by expansion of said mixturein said vessel, said froth rising above said level; f. releasing meansfor releasing said froth from a portion of said space upwardly remotefrom said vessel; and g. rinsing means for applying a film of liquid toan inner face of said riser while keeping the remainder of said spacesubstantially free from said liquid.
 6. Apparatus as set forth in claim5, wherein said rinsing means include a nozzle member directed toward aportion of said inner face contiguously adjacent said releasing meansand offset from the same toward said level.
 7. Apparatus as set forth inclaim 6, wherein said riser has an upright axis, said inner face extendsabout said axis, and said rinsing means include rotating means forrotating said nozzle member about said axis and for thereby sequentiallydirecting said liquid to portions of said inner face angularly offsetrelative to said axis.
 8. Apparatus as set forth in claim 7, whereinsaid rotating means include a tubular member elongated in the directionof said axis, drive means for rotating said tubular member about saidaxis, said tubular member having respective orifices in said space andoutside said space, said nozzle member being attached to said tubularmember in sealing engagement with the orifice of the tubular member insaid space, and means for supplying said liquid to the orifice of saidtubular member outside said space.
 9. Apparatus as set forth in claim 5,wherein said mixing means include a water jet pump and means forconnecting said water jet pump to a source of the water to be purifiedand to ambient air, said feeding means connecting said pump to saidexpansion vessel.